Electric conductor and method

ABSTRACT

The disclosed conductor includes a core, having a plurality of conductive glass fibers, an overwrap of non-conductive glass strands wound under tension around the core and a semiconductive overcoat, preferably of poly tetrafluoroethylene and a suspension of fine conductive powders, preferably graphite or carbon. The overwrap includes distinct windings, rather than a braid, which securely retains the fibers in a cylindrical core, having a uniform cross-section. Further, the overwrap is uniformly wound under tension to provide a matrix of uniform non-insulating apertures or diamond-shaped spaces, assuring uniform conductance between the core and the overcoat.

United States Patent 1191 Deardurff 1*June 18, 1974 1 ELECTRIC CONDUCTOR AND METHOD [75] Inventor: Lawrence R. Deardurff, Newark,

Ohio

[73] Assignee: Owens-Corning Fiberglas Corporation, Toledo, Ohio Notice: The portion of the term of this patent subsequent to Feb. 22, 1989, has been disclaimed.

[22] Filed: Jan. 10, 1973 211 App]. No; 322,311

[52] [1.5. CI 338/214, 156/52, 174/102 SC, 338/66 [51] Int. Cl liQlgQ/OO 581 Field 0fSearch.338/214, 66; 174/130, 102 so,

174/120 R, 110 FC; 156/52 [56] References Cited UNITED STATES PATENTS 3,166,688 l/l965 Rowand ,1 338/214 UX cououcrrvs FIBERS 3,284,751 11/1966 Barker 338/214 X 3,463,871 8/1969 Rogers 174/120 R 3,553,349 1/1971 Heinzmann 174/120 R 3,644,866 l/l97l Deardurff 338/214 Primary Examiner E. A. Goldberg Attorney, Agent, or Firm-Staelin & Overman; Raymond E. Scott [57] ABSTRACT 25 Claims, 3 Drawing Figures 20 ssmcowoucnvs POLYMER PATENIED JUN 1 8 I974 GLASS FIBERS 20 ssmcowoucnvs POLYMER CONDUCTIVE FIBERS 1 ELECTRIC CONDUCTOR AND METHOD FIELD OF THE INVENTION The conductor of this invention is particularly suitable for high temperature applications which require uniform conductance, such as the spark ignition of an automobile. The preferred conductor combines the advantages of conductive glass fibers with the high temperature service capabilities of a semiconductive Teflon overcoat.

The problems of electrical interference with communications, including radio and television, has resulted in certain government standards applicable to automotive ignition cables, for example. Further, the temperature within an automobile hood has increased steadily, due to larger horse power engines and emission control devices, requiring greater temperature service capabilities for all engine components, including ignition cables. These requirements have created an urgent need for ignition cables having high temperature service capabilities and a uniform conductance, which are met by the conductor and method of this invention. Further, the advantages of the electrical conductor of this invention are particularly suitable for other applications, including heating elements for domestic appliances and for extreme service applications, such as driveway and gutter heating elements which are subject to weather,

impact and wear.

The improved electrical conductor of this invention includes a conductive core, means to retain the elements of the core in uniform circular cross-section and means for insuring uniform conductance between the core and a semiconductive overcoat. In the preferred embodiment, the core includes a plurality of conductive fibers, such as the conductive fibers disclosed in US. Pat. No. 3,247,020, which is assigned to the assignee of the instant application. The fibers are securely retained in a cylindrical bundle by winding nonconductive strands, under tension, around the core fibers. The strand windings are preferably distinct, rather than laced, to facilitate stripping of the core and are uniformly spaced to provide a matrix of nonconductive spaces to assure uniform conductance. The semiconductive overcoat preferably includes poly tetrafluoroethylene, because of its high temperature service capabilities and wear resistance and includes a suspension of fine conductive particles, preferably graphite or carbon.

In the preferred embodiment, the overwrap includes two distinct winding layers, rather than a braid, which is easier to strip and provides more uniform spacing between the strands. The spacing is preferably controlled vto between 1/16 and 3/16 inch, measured between cross-over points, which, in combination with the semiconductive overcoat, provides uniform conductance between the overcoat and the core. The thickness of the overwrap may also be more accurately controlled and is preferably between about 0.005 to 0.010 inch.

The poly tetrafluoroethylene overcoat is also easier to strip than conventional synthetic rubber overcoats and reduces or eliminates electrical interference, which it is a prime objective of the disclosed invention. Graphite or carbon particles are preferred because the particles are substantially uniform in size and are commercially available at a lesser expense than other con- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, with cut away portions.

7 showing one embodiment of the electrical conductor of this invention FIG. 2 is a perspective, partially schematic view of the conductive core and the method of winding the overwrap in the manufacture of the electrical conductor shown in FIG. 1; and

FIG.- 3 is an end view of the electrical conductor shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The insulated conductor 20 shown in FIGS. 1 and 3 includes a conductive core 22, a non-conductive overwrap 24 and a semi-conductive overcoat 26. In the preferred embodiment, the core is composed of a plurality of elongated conductive fibers 38, as shown in FIG. 3. The conductive fibers may be formed from strands of glass by the method described in US. Pat. No. 3,269,883, which is assigned to the assignee of the instant application. Reference may also be made to US. Pat. No. 3,247,020.

The overwrap 24 comprises winds of non-conductive strands, such as the glass strands disclosed in US. Pat. NO. 2,333,961 and sold by the assignee of the instant application as E Glass." The strands are preferably wound under tension in distinct layers, rather than braided, as shown in FIG. 2. The first strand 28 is wound around the core under tension to form a first layer 30 and the second strand 32 is wound under tension over the first layer to form a second layer 34, generally perpendicular to the first layer. The winding method shown in FIG. 2 includes two spindles 36 which tension the strands 28 and 32 during winding.

The strands are preferably wound under tension to accurately control the circular cross-section of the fiber bundle 22, which is particularly important in maintaining uniform conductance, as described hereinbelow. As will be noted from FIGS. 1 and 2, the strand windings are preferably spaced on the core 22 to provide a uniform matrix of non-insulating or conductive diamond-shaped openings 37. In the preferred embodiment, the strands are uniformly spaced a distance of H16 to 3/l 6 inch, measured longitudinally on the core from cross-over points the thickness of the overwrap is between about 0.005 to 0.010 inch to provide uniform conductance between the semiconductive overcoat 26 and the conductive core 22.

The strands may be wound on the core in a conventional winding apparatus, such as a double serving unit, at 1 1,000 rpm, for example. A positive tension of about 50 grams has been found particularly suitable to retain the circular cross-section of the core 22. Where the spacing between the strands is greater than threesixteenth of an inch, a Catinary or looping effect occurs between the semiconductive overcoat and the core with corona losses. Where the spacing is smaller, the strike through is limited.

As described above, the winding of the overwrap under tension, is particularly important to the conductor of this invention to maintain the glass fiber core in a cylindrical bundlehaving a uniform cross-section. The uniform cross-section of the bundle assures a more uniform conductance in the conductive roving of this invention and thereby limits stray radiation. The winding of the overwrapin two separate windings makes the overwrap easier to strip, which is particularly important in certain applications of the conductor of this invention. The uniform spacing of the strands, as described above, in combination with the semiconductive overcoat and the uniform thickness of the overwrap also assures uniform conductance.

The overcoat 26 is a uniform layer of a semiconductive material, which forms a radiation shield for the conductor. In the preferred embodiment, the overcoat is a high temperature and friction resistant material having fine particles of a conductive powder suspended therein. The preferred material for the overcoat is a semiconductive poly tetrafluoroethylene, which has at least four advantages in the conductor of this invention: (1 poly tetrafluoroethylene having suspended conductive particles provides an excellent electrical shield, eliminating stray radiation; (2) poly tetrafluoroethylene is easier to strip than conventional synthetic rubber products, eliminating a strip-coat application; (3) poly tetrafluoroethylene has excellent high temperature service capabilities; and (4) poly tetrafluoroethylene protects the core because of its low coefficient of friction. In certain applications, other materials may also be utilized, including Silastic, which is a semiconductive silicone rubber available from Dow Corning Corporation.

The preferred conductive material is a graphite or carbon particulate, although other conductive materials may also be utilized. Graphite is relatively inexpensive and commercially available in uniform size ranges. The preferred maximum size range for the graphite powder is about percent, 1 to 3 microns and 90 percent less than 1 micron.

in the preferred method of forming the overcoat, the core and overwrap are dipped into a poly tetrafluoroethylene solution, wiped by a metal or rubber die and cured in a vertical gas-filled tower. Tetrafluoroethylene is available commercially from E. l. duPont de Nemours Company under the trade name fTeflon. The graphite or carbon particles are added to the Teflon as a dispersion, which may also include a filler, such as silicone, wetting agents, etc. A suitable graphite dispersion, for example, includes 100 parts by volume tetrafluoroethylene, 27.3 parts by volume graphite and 62.7 parts by volume water. The total graphite in this composition is 22 percent by weight. The preferred percentage of graphite in the overcoat is between about 1 l to 90 percent by weight, depending upon the preferred resistance range of the application. In aignition cable, for example, the preferred resistance is about 5,000 ohms per foot, however in a heating element, the preferred resistance is about 150 to 170 ohms per foot. The preferred thickness of the overcoat is about 0.005 to 0.0l0 inches.

The insulated conductor of this invention may then be utilized as an ignition cable, for example, by extruding a primary insulation, such as silicone rubber, over the overcoat, retaining the primary insulation with a fiber glass braid and forming an outer jacket over the braid of a suitable material, including silicone rubber. These subsequent operations are not claimed as part of theelectrical conductor or method of this invention.

The preferred method of manufacturing the insulated electrical conductor 20 of this invention then includes, bundling of a plurality of elongated conductive fibers 38 into a generally cylindrical core 22, as shown in FIG. 2. The number of fibers will depend upon the particular application for the conductor, however a suitable core has 60 conductive glass fibers, each fiber having a diameter of about 0.005 inch, forming a cylindrical core having a diameter of about 0.050 inch. The method then includes winding, under tension, distinct layers (30 and 34) of non-conductive strands 28 and 32, as shown in H6. 2, to securely retain the fibers 38 of the core in a uniform circular cross-section. The strands 28 and 30 are preferably uniformly spaced and angularly wound on the core to provide a matrix of diamondshaped non-insulating apertures 37, uniformly spaced axially and longitudinally on the core to assure uniform conductance between the core 22 and the semiconductive overcoat 26.

Finally, the core and overwrap are encased in a semiconductive overcoat 26, preferably poly tetrafluoroethylene, having fine particles of graphite or carbon suspended therein. In the preferred embodiment, the overcoat includes between about 2 and 30 percent by weight graphite or carbon particles. The semiconductive overcoat may be applied to the core and overwrap by dipping the core in a solution of tetrafluoroethylene, as described above, wiping the overcoat with a metal or rubber die and curing in a vertical tower. A suitable curing temperature for poly tetrafluoroethylene is about 680 F.

The electrical conductor of this invention substantially eliminates interference to television and radio, for example, when utilized as a spark-type ignition cable, as described above. Further, the insulated conductor of this invention is particularly suitable for high temperature service applications, in excess of 450 F, while eliminating stray radiation.

1 claim:

1. An insulated electrical connector, comprising, in combination, an electrically conductive core, an overwrap and a semi-conductive overcoat, said core comprising a plurality of flexible conductive fibers, said overwrap comprising at least one winding substantially evenly distributed on said core, defining a matrix of substantially uniformly spaced non-conductive spaces and retaining said fibers in a cylindrical bundle having a constant cross-section and said overcoat comprising a coating of polymerized tetrafluoroethylene having fine carbon particles suspended therein filling said spaces.

2. The insulated electrical conductor defined in claim 1, characterized in that said overwrap comprises at least two angularly disposed distinct windings of glass strands.

3. The insulated electrical conductor defined in claim 2, characterized in that said apertures are 1/16 to 3/l 6 inch, measured longitudinally between cross-over points.

4. The insulated electrical conductor defined in claim 1, characterized in that said overcoat includes about 2 to 30 percent by weight of said fine carbon particles.

5. An insulated electric cable, comprising, in combination, 'a conductive core including a plurality of elongated flexible fibers, an overwrap retaining said fibers in a cylindrical bundle, comprising at least two noninterlacing layers of non-conductive strands uniformly wound in tension around said fibers to tightly retain said fibers and providing a matrix of non-insulating apertures of substantially uniform size, and a polymeric semiconductive overcoat encasing said cylindrical core and overwrap and substantially filling said apertures, said apertures providing a uniform conductance between said cylindrical conductive core and said semiconductive overcoat.

6. The insulated electric cable defined in claim 5, characterized in that said polymeric semiconductive overcoat comprises a layer of polymerized tetrafluoroethylene having fine graphite particles suspended therein.

7. The insulated electric cable defined in claim 6, characterized in that said overcoat includes about 2 to 30 percent by weight of said fine particles of graphite.

8. The insulated electric cable defined in claim 5, characterized in that the width of said overwrap is about 0.005 to 0.010 inches.

9. The insulated electric cable defined in claim 5, characterized in that said non-insulated apertures are about 1/ 16 to 3/ 16 inches, measured between crossover points of the strands.

10. The insulated electric cable defined in claim 5, characterized in that said flexible fibers are conductive strands of glass and said overwrap strands are nonconductive glass strands.

11. An overcoated conductive roving, comprising, in combination, a plurality of elongated conductive glass fibers securely retained by an overwrap in a cylindrical bundle having uniform cross-section and a semiconductive overcoat encasing said cylindrical core, said overcoat being at least one winding of glass strands forming non-conductive spaces, said overcoat comprising a layer of polymerized tetrafluoroethylene having suspended therein 2 to 30 percent by weight fine carbonaceous particles and said overcoat substantially filling said spaces.

12. The conductive roving defined in claim 11, characterized in that said overwrap is defined by at least two windings of glass strands forming said nonconductive overwrap having a matrix of uniformly spaced conductive apertures.

13. The conductive roving defined in claim 12, characterized in that said overwrap includes at least two angularly disposed distinct windings of glass strands, said windings evenly distributed on said core, in spaced relation, forming a matrix of uniformly spaced nonconducting apertures.

14. The conductive roving defined in claim 13, characterized in that said strands are in tension to securely retain said glass fibers in a uniform cross-section.

15. The conductive roving defined in claim 14, characterized in that the thickness of said overwrap is about 0.005 to 0.010 inch.

16. The conductive roving defined in claim 14, characterized in that the longitudinal spacing between said windings of overwrap strands is about l/l.6 to 3/16 inches.

17. In an elevated temperature ignition cable, the combination of a conductive core comprising a plurality of electrically conductive elongated glass fibers in a cylindrical bundle having a uniform cross-section, said glassfibers securely retained in said cylindrical bundle by at least two angularly disposed distinct windings of glass strands forming a non-conductive overwrap, said windings evenly distributed on said core, in spaced relation, forming a matrix of uniformly spaced nonconductive apertures, and a semi-conductive overcoat enclosing said core and overwrap, and substantially filling said apertures, said overcoat comprising a layer of polymerized tetrafluoroethylene having about 2 to 30 percent, by weight, fine particles of graphite suspended therein.

18; The ignition cable defined in claim 17, characterized in that said glass strands are in tension, about said conductive core, to assure uniform cross-section of said COl'C.

19. The ignition cable defined in claim 17, characterized in that the spacing between said glass strands is about 1/16 to 3/16 inch measured longitudinally on said core between cross-over points.

20. The ignition cable defined in claim 17, characterized in that the thickness of said overwrap is about 0.005 to 0.010 inch.

21. In a method of manufacturing an insulated electrical conductor, the steps of: bundling a plurality of elongated flexible conductive fibers into a cylindrical core, uniformly winding under tension at least two distinct layers of non-conductive strands around said core (1) to securely bind said fibers into a cylindrical core having uniform cross-section and (2) to uniformly space said windings on said core to define a matrix of non-insulating apertures uniformly spaced axially and circumferentially on said core, and encasing said cylindrical core, non-conductive windings and apertures in a semi-conductive polymeric overcoat, said windings thereby providing uniform conductance between said core and said overcoat.

22. The method of manufacturing an insulated electrical conductor defined in claim 21, wherein said core and windings are encased within said semiconductive overcoat by dipping said core and windings in a mixture of polymerized tetrafluoroethylene and a conductive powder and curing said polymerized tetrafluoroethylene.

23. The method of manufacturing an insulated electrical conductor defined in claim 22, including the step of wiping the uncured polymerized tetrafluoroethylene mixture, prior to curing.

24. The method of manufacturing an insulated electrical conductor defined in claim 21, including individually winding strands of non-conductive glass around a core of conductive glass fibers.

25. An insulated electric cable comprising, in combination a conductive core including a plurality of flexible fibers, an overwrap containing said fibers in a cylindrical bundle comprising; at least two non-interlacing layers of non-conductive continuous linear elements uniformly wound under tension in tight retaining relation about said core fibers and providing a porosity of substantially uniform magnitude along the length of said overwrap, and a semiconductive overcoat of flexible material permeating said overwrap and communicating with said cylindrical conductive core such that a substantially uniform conductance is established between the semiconductive overcoat material and conductive core along its length. 

2. The insulated electrical conductor defined in claim 1, characterized in that said overwrap comprises at least two angularly disposed distinct windings of glass strands.
 3. The insulated electrical conductor defined in claim 2, characterized in that said apertures are 1/16 to 3/16 inch, measured longitudinally between cross-over points.
 4. The insulated electrical conductor defined in claim 1, characterized in that said overcoat includes about 2 to 30 percent by weight of said fine carbon particles.
 5. An insulated electric cable, comprising, in combination, a conductive core including a plurality of elongated flexible fibers, an overwrap retaining said fibers in a cylindrical bundle, comprising at least two non-interlacing layers of non-conductive strands uniformly wound in tension around said fibers to tightly retain said fibers and providing a matrix of non-insulating apertures of substantially uniform size, and a polymeric semiconductive overcoat encasing said cylindrical core and overwrap and substantially filling said apertures, said apertures providing a uniform conductance between said cylindrical conductive core and said semiconductive overcoat.
 6. The insulated electric cable defined in claim 5, characterized in that said polymeric semiconductive overcoat comprises a layer of polymerized tetrafluoroethylene having fine graphite particles suspended therein.
 7. The insulated electric cable defined in claim 6, characterized in that said overcoat includes about 2 to 30 percent by weight of said fine particles of graphite.
 8. The insulated electric cable defined in claim 5, characterized in that the width of said overwrap is about 0.005 to 0.010 inches.
 9. The insulated electric cabLe defined in claim 5, characterized in that said non-insulated apertures are about 1/16 to 3/16 inches, measured between cross-over points of the strands.
 10. The insulated electric cable defined in claim 5, characterized in that said flexible fibers are conductive strands of glass and said overwrap strands are non-conductive glass strands.
 11. An overcoated conductive roving, comprising, in combination, a plurality of elongated conductive glass fibers securely retained by an overwrap in a cylindrical bundle having uniform cross-section and a semi-conductive overcoat encasing said cylindrical core, said overcoat being at least one winding of glass strands forming non-conductive spaces, said overcoat comprising a layer of polymerized tetrafluoroethylene having suspended therein 2 to 30 percent by weight fine carbonaceous particles and said overcoat substantially filling said spaces.
 12. The conductive roving defined in claim 11, characterized in that said overwrap is defined by at least two windings of glass strands forming said non-conductive overwrap having a matrix of uniformly spaced conductive apertures.
 13. The conductive roving defined in claim 12, characterized in that said overwrap includes at least two angularly disposed distinct windings of glass strands, said windings evenly distributed on said core, in spaced relation, forming a matrix of uniformly spaced non-conducting apertures.
 14. The conductive roving defined in claim 13, characterized in that said strands are in tension to securely retain said glass fibers in a uniform cross-section.
 15. The conductive roving defined in claim 14, characterized in that the thickness of said overwrap is about 0.005 to 0.010 inch.
 16. The conductive roving defined in claim 14, characterized in that the longitudinal spacing between said windings of overwrap strands is about 1/16 to 3/16 inches.
 17. In an elevated temperature ignition cable, the combination of a conductive core comprising a plurality of electrically conductive elongated glass fibers in a cylindrical bundle having a uniform cross-section, said glass fibers securely retained in said cylindrical bundle by at least two angularly disposed distinct windings of glass strands forming a non-conductive overwrap, said windings evenly distributed on said core, in spaced relation, forming a matrix of uniformly spaced non-conductive apertures, and a semi-conductive overcoat enclosing said core and overwrap, and substantially filling said apertures, said overcoat comprising a layer of polymerized tetrafluoroethylene having about 2 to 30 percent, by weight, fine particles of graphite suspended therein.
 18. The ignition cable defined in claim 17, characterized in that said glass strands are in tension, about said conductive core, to assure uniform cross-section of said core.
 19. The ignition cable defined in claim 17, characterized in that the spacing between said glass strands is about 1/16 to 3/16 inch measured longitudinally on said core between cross-over points.
 20. The ignition cable defined in claim 17, characterized in that the thickness of said overwrap is about 0.005 to 0.010 inch.
 21. In a method of manufacturing an insulated electrical conductor, the steps of: bundling a plurality of elongated flexible conductive fibers into a cylindrical core, uniformly winding under tension at least two distinct layers of non-conductive strands around said core (1) to securely bind said fibers into a cylindrical core having uniform cross-section and (2) to uniformly space said windings on said core to define a matrix of non-insulating apertures uniformly spaced axially and circumferentially on said core, and encasing said cylindrical core, non-conductive windings and apertures in a semi-conductive polymeric overcoat, said windings thereby providing uniform conductance between said core and said overcoat.
 22. The method of manufacturing an insulated electrIcal conductor defined in claim 21, wherein said core and windings are encased within said semiconductive overcoat by dipping said core and windings in a mixture of polymerized tetrafluoroethylene and a conductive powder and curing said polymerized tetrafluoroethylene.
 23. The method of manufacturing an insulated electrical conductor defined in claim 22, including the step of wiping the uncured polymerized tetrafluoroethylene mixture, prior to curing.
 24. The method of manufacturing an insulated electrical conductor defined in claim 21, including individually winding strands of non-conductive glass around a core of conductive glass fibers.
 25. An insulated electric cable comprising, in combination a conductive core including a plurality of flexible fibers, an overwrap containing said fibers in a cylindrical bundle comprising; at least two non-interlacing layers of non-conductive continuous linear elements uniformly wound under tension in tight retaining relation about said core fibers and providing a porosity of substantially uniform magnitude along the length of said overwrap, and a semiconductive overcoat of flexible material permeating said overwrap and communicating with said cylindrical conductive core such that a substantially uniform conductance is established between the semiconductive overcoat material and conductive core along its length. 